Limited supply of conventional food protein is a major problem facing a rapid increase in world population. Of particular importance is the production of animals that contain proteins having essential amino acids required by humans. Due to limited production facilities and lack of improvement in production technology, increase in animal protein production does not seem to be proportionate the increase in world population.
Therefore, it appears highly desirable to improve the productivity of animal protein production. One of the means to improve the productivity is to develop feed compositions that enhance animal growth.
It is known that the growth rate of animals can be accelerated by administration of certain classes of substances such as antibiotics, surfactants, and estrogens. The administration of each of these classes of substances had disadvantages, however, which have prevented their universal acceptance. Thus, it is believed that antibiotics and surfactants, while effective under certain conditions, principally act to suppress diseases and do not elicit a true growth response. It is for that reason that such use of antibiotics will be limited in Europe, whereas it is under debate in the USA and Asia.
Also, the use of estrogens as growth-promoting agents presents certain inherent difficulties and hazards. Thus, estrogens frequently downgrade the animal to which they are administered. Another disadvantage is that some of the estrogenic material may remain in the edible portions of the animal and could presumably produce an adverse effect on an individual when consumed. Further, the known substances have principally been administered by injection or implantation procedures, which are both costly and time-consuming and are often disliked by consumers.